Process for producing flame-retardant acrylic fibers

ABSTRACT

A process for preparing flame-retardant acrylic fibers which comprises (a) preparing an acrylic fiber gel containing fine particles of vinyl halide or vinylidene halide polymers by wetspinning, (b) treating the fiber gel with organic phosphates and/or phosphonates, and (c) thereafter stretching the fiber gel in hot water. Thus obtained fibers have an excellent flame resistance, high luster and improved strength.

1.1111100 States Patent 1191 Takeya et a1.

[ Dec. 17, 1974 [75] Inventors: Kenji Takeya, Okayama; Toshiyuki Kohashi; Kenichi Masuhara, both of Okayama-ken, all of Japan 173] Assignee: Japan Exlan Company Limited,

Osaka, Japan [22] Filed: Mar. 13, 1973 [211 Appl. No.: 340,888

[30] Foreign Application Priority Data Mar. 21, 1972 Japan 47-28295 [52] US Cl. 264/210 F, 8/130.1, 117/7, 117/137, 260/296 AN, 264/136, 264/182, 264/343 [51] Int. Cl. D0lf 3/10 [58] Field of Search 264/182, 343, 130, 210 F, 264/136, 29.6 AN, 29.6 AQ; 106/15 FP; 117/143, 137, 136, 7; 8/115.5, 130.1

[56] References Cited UNITED STATES PATENTS 3,164,650 l/1965 Kosay et a1. 264/130 3,193,602 7/1965 Leonard et al. 3,222,118 12/1965 Coleman 3,242,124 3/1966 Lowes et a1 264/182 3,410,819 11/1968 Koorty et a1 264/182 3,451,960 6/1969 Schmidt 260/296 AQ 3,485,913 12/1969 Yamada et a1 264/264 3,560,423 2/1971 Levesque et al.... 264/182 3,580,735 5/1971 Shimodoi et al.... 264/182 3,582,258 6/1971 Coleman I 117/137 3,645,964 2/1972 Pietro 106/15 FP 3,660,351 5/1972 Schmidt et ill. 260/296 AN 3,682,692 8/1972 Lamson et al. 117/137 3,729,434 4/1973 Todd 1 117/137 3,759,851 9/1973 Carl et a1. 106/15 FP FOREIGN PATENTS OR APPLICATIONS Primary Examiner-Jay H. Woo Attorney, Agent, or Firm-Wenderoth, Lind & Ponack 5 7 ABSTRACT (c) thereafter stretching the fiber gel in hot water.-

Thus obtained fibers have anexcellenttlame resistance, high'luster and improved strength.

10 Claims, N0 Drawings 12/1970 Japan 264/182 PROCESS FOR PRODUCING FLAME-RETARDANT ACRYLIC FIBERS step, by wet spinning a spinning solution, which consists of acrylonitrile homoor copolymers and a concentrated aqueous solution of thiocyanate, containing finely dispersed polymers selected from the group consisting of vinyl halide homoand co-polymer and vinylidene halide homovand co-polymer (hereinafter referred to as halogen-containing polymer) in the usual way to obtain a fiber inv a hydrogelcondition, treating the thus obtained fiber with a specified organic phosphate and/or organic phosphnate, and then stretching the fiber at least three times its initial length in hot water above 90C., or contingently by subjecting the stretched fiber to an ordinary fiber structure collapsing treatment by drying, and further subjecting the fiber to specified wet heat or dry heat stretching.

The fibers produced from the ordinary acrylonitrile homopolymer or copolymer are widely used in textile and home furnishings uses. However, because of essential lack in flame resistance of these fibers, their use in specialpurposes, for example home furnishings such as carpets and curtains and the like'and clothing for babites and children is not desirable.

Thus, for the purpose of overcoming this defect of acrylic fibers there have been heretofore proposed a number of methods such as a method of copolymerizing 'a flame retardant monomer with acrylonitrile, a method of blend-spinning a flame retardant polymer with acrylonitrile homopolymer or copolymer, a method of spinning a spinning solution into which a flame retardant has been added, a method of aftertreating the fiber with a'flame retardant and the like.

A more concrete technique of such flame retardant methods is to spin an acrylicspinning solution into which-powder of halogen-containing polymer such as polyvinylchloride, polyvinylidene chloride, etc. has been added.

In the conventionalprocess for producing the acrylic fiber containing such halogen-containing polymer by wet-spinning an acrylonitrile polymer solution containing dispersed particles of a halogen-containing polymer such as polyvinyl chloride and prepared by the use of a solvent which is not able'to swell'nor dissolve the halogen-containing polymer, the fiber obtained has many voids withinthe fiber, since there is no compatibility between the halogen-containing polymer and the acrylonitrile polymer. The existence of such voids results in an excessive decrease in the strength of the fiber and causes devitrification, namely the loss of transparency to make the fiber opaque, thus making the fiber of extremely low quality.

To prevent these defects, Japanese Patent Publication No. 35974/1971 discloses a method wherein there is spun an acrylic spinning solution using aqueous solution of zinc chloride as the solvent for the acrylic polymer and containing a halogen-containing polymer as well as a tris(polyhaloalkyl) phosphate compatible with prevented from devitr ification and the halogen-containing polymer, in a dispersed condition.

However, in the solution of acrylonitrile polymer dissolved in concentrated aqueous solution of thiocya-' nate, which is a strong electrolyte, as the solvent for the acrylonitrile polymer, in the event that the halogencontaining polymer particles are present together with the particles of the phosphate, the particles of each kind are not able to be present in a stable condition independently of each other. That is, the halogencontaining polymer particles are made to swell by the phosphate and the swollen particles aggregate into masses which cause various troubles such as filter clogging, spinnerette clogging and the like. Thus, the use of the foregoing method is extremely difficult.

Thus, we made an intensive study to remove the above mentioned defects caused in introducing the halogen-containing polymer into the acrylic fiber in the production of the fiber using concentrated aqueous so-,

lution thiocyanate as the solvent. As a result, we have found that, by wet-spinning in the usual way an acrylic spinning solution, which consists of acrylontrile polymers and aqueous concentrated solution of thiocyanate, in which the halogen-containing polymer is finely dispersed, treating the thusobtained fiber in a hydrogel condition with a specified compound, and then stretching the fiber under heat under specified conditions, or contingently subjecting the stretched fiber to additional wet heat stretching or dry heat stretching, the various troubles in the spinning step can be removed, the fiber can be satisfactorily prevented from devitrification, improved in strength and luster, and furthermore given good flame retardance. The present invention has been accomplished on the'basis of this finding.

The main object of the present invention is to provide an improved process for producing flame retardant acrylic fibers.

An object of the invention is to prevent the devitrification of the acrylic fiber containing the halogen containing polymer as well as to improve the various properties of the fiber, such as strength, luster, etc.

Another object of the invention is to produce an acrylic fiber having an excellent flame retardant effect, improved in strength and luster, industrially advantageously, without causing any troubles in the spinning step, by treating the acrylic fiber gel in a hydrogel condition containing the halogen-containing polymer particles, obtained by wet-spinning a spinning solutionof an acrylonitrile polymer dissolved in a concentrated aqueoussolution of thiocyanate, with a specified compound, stretching the fiber under heat under specified conditions, or contingently by subjecting the stretched fiber to additional wet heat stretching .or dry heat stretching.

Further objects of-the invention will become apparent from the following concrete explanations.

These objects of the present invention can be attained by treating the fiber in a hydrogel condition obtained by wet-spinning a spinning solution, of acrylonitrile polymer dissolved in a concentrated aqueous thiostretching the fiber at least three times the initial length in hot water above 90C. Or, the above-mentioned objects of the invention can be more satisfactorily attained by stretching the foregoing heat-stretched fiber, after subjecting it to an ordinary fiber structure collapsing by drying, less than three times the stretched fiber length under wet heat at a temperature above 100C. or under dry heat above 140C.

In the production of the acrylic fiber using a concentrated aqueous thiocyanate solution as the solvent for the polymer, in the event of introducing the halogencontaining polymer into the fiber, it has become possible by the use of the process of the present invention to produce an acrylic fiber having very good flame retardance, prevented from devitrification and improved in fiber properties such as strength and luster, industrially advantageously, while avoiding various troubles in the spinning step, such as filter clogging, spinnerette clogging, filament breaking and the like.

In the fiber of the wet-spun hydrogel condition acrylic fiber, the halogen-containing polymer is present in the form of fine particles. When the fiber in such a condition is subjected to treatment with the specified compound according to the present invention and heat stretching under specified conditions, or contingently to additional wet heat or dry heat stretching, the halogen-containing polymer particles in the fiber are stretched after being swollen and plasticized. Thus, it is supposed that the particles will become combined with each other to form streams in the fiber and the fiber can be prevented well from devitrification and improved in strength and luster.

As opposed thereto, in the event that the fiber is not treated with the specified organic phosphate and/or organic phosphonate according to the present invention and subjected only to heat stretching or heat stretching followed by additional wet heat or dry heat stretching, it is supposed that the halogen-containing polymer particles present in the hydrogel condition fiber will remain in that form even after stretching so that devitrification takes place, and various fiber properties such as strength, etc. are impaired.

Also, the halogen-containing polymer particles are contained in the fiber in a more or less aggregated condition and such aggregates remaining in that form without being destroyed after passing through the aftertreatment steps, such as stretching, drying and the like, will cause the devitrification of the fiber and the impairment of the fiber properties.

Since the phosphates and phosphonates used in the present invention contribute to the flame retardance of the fiber synergetically with the halogen-containing polymer, the acrylic fiber obtained according to the present invention becomes to have very good flame retardance.

The hydrogel condition acrylic fiber used in the present invention containing the halogen-containing polymer can be obtained in the usual way by wet-spinning a spinning solution, of an acrylonitrile polymer dissolved in a concentrated aqueous thiocyanate solution, containing the finely, dispersed halogen-containing polymer, Concretely, for example the spinning method described in U.S. Pat. Nos. 2,558,730, 2,558,731, etc. can be used. The filaments extruded-and formed in the 'aqueous coagulation bath in the usual way become swollen filaments in a hydrogel condition which will be then subjected to the treatment and heat stretching according to the present invention, by being washed with water and, as required, subjected to stretching from about 1.5 to about 3 times at ordinary temperature before or after the water-washing.

The organic phosphate compounds and/or organic phosphonate compounds which are made to cover or steep the acrylic fiber in a hydrogel condition to act as a binder between the halogen-containing polymer and the acrylonitrile polymer entirely incompatible with each other and prevent the devitrification of the fiber and the decrease in the fiber strength due to the introduction of the halogen-containing polymer in the fiber, and which promote the orientation of the halogencontaining polymer'to improve the fiber qualities, are

compounds capable of dissolving, swelling or plasticizing the halogen-containing polymer.

More concretely, they are the compounds represented by the following general formula:

or the condensation products of these compounds, wherein R R R R R and R are each alkyl group having one to 20 carbonjatoms, haloalkyl group having one to 20 carbon atoms, alkenyl group having one to 20 carbon atoms, arylalkyl group having seven to 20 carbon atoms, alkylaryl group having seven to 20 carbon atoms, or aryl group and may be the same with or different from each other and R, may be hydrogen atom or wherein R is alkylene group having one to six carbon atoms or haloalkylene group having one to six carbon atoms, and R and R are each a same organic residue as R, to R For example, there canbe mentioned tributyl phosphate, trioctyl phosphate, triphenyl phosphate, tribenzyl phosphate, tricreasyl phosphate, tris(2,3- dibromopropyl)-phosphate, tris(2,3- dichloropropyl)phosphate, tris(chlorobromomethyl)- phosphate, tris(bromochloropropyl)phosphate, tris(2-chloroethyl)phosphate, bisdibromopropylidichloroporpyl phosphate, bisbromochloropropylbromochloropropyl bisdibromopropyldichloropropyl bisdibromopropyldibromopropyl phosphonate, bis-Z-chloroethylvinyl phosphonate,

(J10 IIQCHzO .III (H) O UHzC H O Ill (11) UHzCHgCl,

etc. Among such phosphates and phosphonates particularly suitably used in the present invention are those having, as R, to R substituents. organic residues containing no halogen atom, such as alkyl group, alkenyl group, aralkyl group, aryl group or alkylaryl group; or mixtures containing such a compound as the major component and another phosphate or phosphonate in a minor ratio.

Such phosphates and/or phosphonates according to the present invention are made to impregnate the acrylic fiber in a hydrogel condition, directly as such as a solution or dispersion in water, organic solvent or other suitable solvents, by spraying or immersing, etc. Suitably, the amount of absorption by the compound in the fiber in such treatment is generally l0 to 80 percent by weight, preferably to percent by weight based on the weight of the halogen-containing polymer present in the fiber. In the event that the amount of application of at least a phosphate and/or at least a phosphonate to the fiber is too small, the objects and effects of the present invention are not fully attained. Also, when the amount is too much, the halogen-containing polymer is excessively softened, with the result that the compound not only does not contribute to the improvement in the fiber qualities but also becomes a cause of re-devitrification of the fiber by being removed in the after-treatment step or during washing.

In the present invention, the acrylic fiber in a hydrogel condition containing the halogen-containing polymer softened or swollen by treatment with such a phosphate and/or phosphonate is stretched at'least three times up to less than about seven times the initial length in hot water above C.,preferably from to C. By such stretching, the fine particles of the halogencontaining polymer or the aggregates of the particles are united and formed into streams so that the devitrification of the fiber is prevented and the fiber properties such as strength, etc. are improved. Such heat stretching conditions are the essential requirements for attaining the foregoing effects, and in heat stretching using any conditions outside this range, the objects and effects of the present invention are not fully attained.

The fiber after having undergone the treatment and heat stretching according to the present invention is subjected to after-treatments such as theordinary fiber structure collapsing treatment by drying, crimping treatment, relaxing heat treatment, to produce the final product fiber. In the present invention, however, it is another procedure to subject the thus heat stretched and structure collapsed fiber to specified additional wet heator dry heat-stretching to attain the objects and effects of the inventionmore fully.

The treatment for the fiber structure collapsing is generally conducted by drying the fiber in an atmosphere of a dry-bulb temperature of 90 C. and wet-bulb temperature of 5090C.

That is, in addition to the above-mentioned phosphate and/or phosphonate treatment and heat stretching, by being subjected to a specified wet heator dry heat-stretching, the halogen-containing polymer in the fiber is distributed and oriented in the form of more stable streams, so that the fiber is made more transparent and prevented from the devitrification more satisfacto-' rily, and furthermore remarkably improved in the physical properties such as strength and lu'ster.

- Desirably, such wet-stretching is carried out .in a heated steam atmosphere at least above 100C., preferably at 105 to C., and the dry heat-stretching, at a temperature at least above 140C, preferably to 220C., by means of heated rolls, heated plates or heated air. The stretching times is desirably less than three times, preferably from 1.1 to 2.5 times, in either case of wet heat-stretching or dry heat-stretching. In the event of using a stretching temperature or stretching times outside such limits, thorough attainment of in the conventional acrylic fiber containing the halogen-containing polymer and the impairment of various fiber qualities-such as strength and luster can be advantageously prevented, and various troubles in the spinning step such as filter clogging and spinnerette clogging caused in the conventional method, for example Japanese Patent Publications No. 35974/l97l wherein a special compound is mixed with the spinning solution, can be avoided.

The acrylonitrile copolymers to be used in the present invention are those containing at least 70 percent, by weight, based on the total weight of the polymer, of acrylonitrile and the balance of one or more monomers copolymerizable therewith and containing one CH =C group. Illustrative monomers include, for example, vinyl esters, such as vinyl acetate, vinyl p'ropionate, and vinyl butyrate; vinyl halides and vinylidene halides, suchas vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene bromide, and vinylidene fluoride; allyl alcohols, such as allyl alcohol, methallyl alcohol, and ethallyl alcohol; allyl, methallyl, and other unsaturated monohydric alcohol esters of monobasic acids, such as allyl and methallyl acetates andlaurates; acrylic acids and alkacrylic acids, suchas acrylic acid,

methacylic acid and ethacrylic acid; esters and amides of the foregoing acids, suchas methyl, ethyl propyl, and

butyl acrylates and methacrylates, acrylamide, methacrylamide, N-methyl, N-eth-yLN-prop yl, and N-butyl acrylamides and methacrylamides; methacrylonitrile, ethacrylonitrile and other hydrocarbon-substituted acrylonitriles; unsaturated sulfonic acids and their salts, such as allylsulfonic acid, methallylsulfonic acid, styrene sulfonic acid and their sodium and potassium salts; unsaturated aliphatic hydrocarbons, such as isobutylene; and numerous other compounds having one group therein, In addition, alkyl esters, for example, of a,B-unsaturated polycarboxylic --acids, such as dimethyl, diethyl, dipropyl, and dibutyl esters of maleic,

fumaric, and citraconic acids produce useful copolymers with acrylonitrile. In preferred instances the polymer will contain at least 80 percent, by weight, of acrylonitrile, based on the total weight of the polymer.

mined from the viscosity in dimethylformamide of the polymer and use of the Staudinger equation (see U.S.

Pat. No. 2,404,713).

The polymers of vinyl halide or vinylidene halide (halogen-containingpolymers) to be introduced into the spinning solution are homopolymers of vinyl halide such as vinyl chloride, vinyl bromide; homopolymers of vinylidene halide such as vinylidene chloride, vinylidene bromide; copolymers of vinyl halide and vinlidene halide; copolymers of vinyl halide or vinylidene halide and less than about 25 percent of acrylonitrile or any of the abovementioned compounds copolymerizable with acrylonitrile.

Such a halogen-containing polymer is finely dispersed in a concentrated aqueous thiocyanate solution of the acrylonitrile polymer in a suitable way to produce the acrylic spinning solution to be used in the present invention.

In dispersing the halogen-containing polymer, any method may be used if the polymer can be finely dispersed in the above-mentioned acrylonitrile polymer solution. However, by the use of our Japanese Patent Application No. 2650/1972, the industrial significance of the invention is further increased.

The preferred amount of introduction of the halogencontaining polymer to be acrylonitrile spinning solution is generally 10 to 120 percent, preferably 30 to 100 percent, by weight based on the weight of the acrylonitrile polymer present in the spinning solution.

The concentrated aqueous thiocyanate solution which dissolve the acrylonitrile polymer to produce the spinning solution are those of well-known composition used as the solvent in acrylic fiber production, and are concentrated (e.g. 35 60 percent) aqueous solutions of, for example, sodium thiocyanate, potassium thiocyanate, ammonium thiocyanate, calcium thiocyanate, etc.

The following examples are for better explanation of the present invention and are not intended to limit the scope of the invention. The parts and percentages in the examples are by weight unless otherwise indicated.

EXAMPLE 1 Five hundred parts of polyvinyl chloride emulsion (30 percent in polymer concentrated) obtained by emulsion polymerization, having an average degree of polymerization of 1,000 and an average particle diameter of 0.26 microns, to which 10 parts of polyoxyethyl' ene lauryl ether, a-nonionic surfactant, having a HLB value of 11.3 had been added, was continuously injected intoa 44 percent sodium thiocyanate solution of an acrylonitrile copolymer 10 percent in polymer concentration.) consisting of 90 percent acrylonitrile and 10 percent methyl acrylate such that the ratio of the emulsion to the polymer solution is 1:10 (by weight), according to the method of Japanese Patent Application No. 2650/1972. The mixture was blended and stirred by means of an in-line high shear mixer (Pipe Line Homomixer manufactured by Tokushu Kikakogyo Co., Japan) to obtain an acrylic spinning solution continuously and stably in which the polyvinyl chloride particles were dispersed finely and uniformly.

The thus-obtained spinning solution as extruded and coagulated in a coagulation bath of a l2'percent aqueous sodium thiocyanate solution at C. through a spinnerette having 50 orifices, each 0.12 mm. in diameter.

The resulting fiber was stretched twice the initial length in room temperature and washed with water. The thusobtained fiber in a hydrogel condition was immersed in a tricresyl phosphate solution for seconds, stretched five times in boiling water at about 99C., and dried in an atmosphere of dry bulb temperature of 120C. and wet bulb temperature of 65C. In this way an acrylic fiber having good luster, substantially free from voids and accordingly substantially without appreciable devitrification, was obtained.

The analysis of this acrylic fiber showed that the fiber contained 23 percent polyvinyl chloride and 12 percent tricresyl phosphate. In spite of a large amount of introduction of polyvinyl chloride, the fiber had a strength of 3.2 g/d and an elongation of 41 percent, which were comparable to those of the ordinary acrylic fiber. By

microscopic examination of the longitudinal section of the fiber, it was observed that the polyvinyl chloride was distributed and oriented in the fiber in the form of streams. Also, as a result of flame retardance tests, the fiber was verified to have good self-extinguishability.

On the other hand, when the above experiment was repeated except that the tricresyl phosphate was excluded, the thus obtained fiber had a large number of voids, showed extreme devitrification, and had a strength as low as 2.1 g/d, thus the fiber being of very low quality. When the longitudinal section of this fiber was viewed under the microscope, the polyvinyl chloride in thefiber was found present in the form of particles.

Five hundred parts of the above-mentioned polyvinyl 'chloride emulsion to which 10 parts polyoxyethylene lauryl ether and 50 parts tricresyl phosphate had been added was mixed in the acrylonitrile polymer solution to prepare an acrylic spinning solution according to the above-mentioned method. The thus obtained spinning solution was wet-spun according to the abovementioned method. However, after a short time from the beginning of spinning, the back pressure on the spinnerette became so much increased that the spinning was made impossible. Upon overhauling the spinnerette head after spinning, the spinnerette orifices and filter were found clogged with masses of swollen partiv cles of polyvinyl chloride. Also, microscopic examination of the spinning solution showed that polyvinyl chloride particles in the spinning solution were swollen into masses by the tricresyl phosphate.

EXAMPLE 2 The acrylic spinning solution produced in Example 1 was extruded and coagulated and the coagulated fiber was stretched in room temperature and washed with water, under'the same conditions as in Example 1.

Thereafter, the fiber was immersed in a tributyl phosphate solution for 10 seconds and then stretched five times in boiling water at about C. The thus obtained acrylic fiber had good luster, was substantially free from devitrification and had the same degree of .transparency as the ordinary transparent fiber. The

fiber containing 23 percent polyvinyl chloride and 15 percent tributyl phosphate and showed good flame retardance.

EXAMPLE 3 The fiber in a hydogel condition as obtained in Example l was treated with bis-2-chloroethyl vinyl phosphate, i.e.

then stretched four times in boiling water at about 100C., and dried in an atmosphere of dry bulb temperature of C. and wet bulb temperature of 65C. An

EXAMPLE 4 The acrylic fiber which had been subjected to the tricresyl phosphate treatment, heat stretching treatment and fiber structure condensation treatment by drying as in Example 1, was further subjected to 1.5 times dry heat stretching in contact with heated plates at 210C.

EXAMPLE-5 To a vinyl chloride-vinylidene chloride copolymer emulsion (40 percent in polymer concentration) obtained by emulsion polymerization, 1 percent by weight of polyoxyethylene lauryl ether (having a HLB value of 1 1.3) based on the weight of the copolymer was added to make the surface of the emulsion particles covered 7 by that surfactant. The thus obtained emulsion was introduced continuously into a 44 percent aqueous thiocyanate solution of an acrylonitrile copolymer consisting of 91 percent acrylonitrile and 9 percent vinyl acetate (10 percent in polymer concentration) such that the ratio of the emulsion to the polymer solution was 1:10 (by weight). The mixture was blended and stirred by means of an in-line high shear mixer to obtain an acrylic spinning solution continuously and stably in l which the particles of the vinyl chloride-vinylidene chloride copolymer were dispersed finely and uniformly.

According to the method of Example 1, the thus obtained spinning solution was spun and the resulting fiber was washed with water to form a fiber in a hydrogel condition. The fiber was immersed in a trioctyl phosphate solution or tribenzyl phosphate solution for 10 seconds, then stretched 5.5 times the initial length in boiling water at about 100C. and dried in an atmosphere of dry bulb temperature of 123C. and wet bulb zyl phosphate. Also, the fiber had a strength of 3.0 g/d and an elongation of 43 percent, thus retaining good fiber qualities in spite of introduction ofa large amount of halogen-containing polymer. Furthermore, it was verified that the halogen-containing polymer in the fiber was formed into streams by microscopic examination and that the fiber represented good self-extinguishability in flame retardance tests.

The thus obtained fiber after the phosphate treatment, heat stretching a'ndfiber structure condensing treatment by drying, was further subjected to 1.4 times dry heat stretching at 200C. using heated rolls or 1.2 times wet heat stretching at l 18C. in heated stream. An acrylic fiber having remarkably improved luster and further improved stream shape of vinyl chloridevinylidene chloride copolymer and without substantially appreciable devitrification was obtained.

EXAMPLE 6 Example 2 was repeated except that a mixture solution consisting of percent tributyl phosphate and 30 percent tris( l-bromo-3-chloroisopropyl)phosphate' was used in place of the single tributyl phosphate solution used in Example 2. As the result, an acrylic fiber having good luster, no substantial devitrification and yet good flame retardance was obtained.

What is claimed is:

1. An improved process for producing flameretardant acrylic fibers which comprises a. preparing acrylic fibers in a'hydrogel condition by wet-spinning aspinning solution, which consists of acrylonitrile homoor co-polymers and a concentrated aqueous solution of thiocyanate, containing finely dispersed particles of a halogen-containing polymer selected from the group of homoand copolymers of vinyl halide and homoand copolymers of vinylidene halide,

b. treating said acrylic fibers in a hydrogel condition with at least one organic compound, whichcan dissolve, swell or plasticize the halogen-containing polymer, selected from the group of an organic phosphate and an organic phosphonate respectively represented by the following general formulas (l) and (11) 1 wherein R R R R R5 and R each are alkyl group having one to 20 carbon atoms, haloalkyl group having one to 20 carbon, atoms,.alkenyl group having one to 20 carbon atoms, arylalkyl group having seven to 20 carbon atoms, alkylaryl group having seven to 20 carbon atoms, or aryl group and may be the same with or different from each other and R may be hydrogen atom or times its initial mer, and the balance of one or more comonomers copolymerizable therewith.

3. The process of claim 1 wherein the halogencontaining polymer is polyvinyl chloride.

4. The process of claim 1 wherein the halogencontaining polymer is a copolymer of vinyl chloride and vinylidene chloride.

5. The process of claim 1 wherein an amount of halogen-containing polymer to add to the spinning solution is 10 to 120 percent by weight based on the weight of the acrylonitrile polymer present in the spinning solution.

6. The process of claim wherein the amount of halogen-containing polymer is 30 to 100 percent by weight based on the weight of acrylonitrile polymer present in the spinning solution.

7. The process of claim 1 wherein said organic compound is selected from the group of tributyl phosphate, trioctyl phosphate, triphenylphosphate, t'ribenzyl phosphate, tricresyl phosphate, tris(2,3- dibromopropyl)phosphate, tris(2,3- dichloropropyl)phosphate, tris(chlorobromoethyl)- phosphate, tris(bromochloropropyl)phosphate, tris(2-chloroethyl)phosphate, bisdibromopropyldichloropropyl phosphate, bisbromochloropropylbromochloropropyl phosphate, bisdibromopropylidibromopropyl phosphonate, bis-2-chloroethylvinyl phosphonate,

Cl CHzClIzO P (II) OCH CH OPODCIhCH Cl and ((IICH CIIUICH OLlfi Clllit'cllzli(0CllzCIIB1CHzCU2 8. The process of claim 1 wherein the amount of absorption of the organic compound in the fiber in such treatment is to 80 percent by weight based on the weight of the halogen-containing polymer present in the fiber.

9. An improved process for producing flameretardant acrylic fibers which comprises a. preparing acrylic fibers in a hydrogel condition by wet-spinning a spinning solution, which consists of acrylonitrile homoor co-polymers and a concentrated aqueous solution of thiocyanate, containing finely dispersed particles of a halogen-containing polymer selected from the group of homoand copolymers of vinyl halide and homoand co-. polymers of vinylidene halide,

b. treating said acrylic fibers in a hydrogel condition with at least one organic compound, which can dissolve, swell or plasticize the halogen-containing polymer, selected from the group of an organic phosphate and an organic phosphonate respectively represented by the following general formula (I) and (II) wherein R R R R R and R each are alkyl group having one to carbon atoms, haloalkyl group having one to 20 carbon atoms, alkynyl wherein R is alkylene group having one to six carbon atoms or haloalkylene group having one to six carbon atoms, and R and R each are same group as R to R c. stretching at least three times its initial length in hot water above C.,

d. subjecting to a fiber structurecollapsing treatment by drying, and

e. thereafter wet heat-stretching less than three times at a temperature above C.

10. An improved process for producing flameretardant acrylic fibers which comprises a. preparing acrylic fibers in a hydrogel condition by wet-spinning a spinning solution, which consists of acrylonitrile homoor co-polymers and a concentrated aqueous solution of thiocyanate, containing finely dispersed particles of a halogen-containing polymer selected from the group of homoand copolymers of vinyl halide and homoand co-' polymers of vinylidene halide,

b. treating said acrylic fibers in a hydrogel condition with at least one organic compound, which can dissolve, swell or plasticize the halogen-containing polymer, selected from the group of an organic phosphate and an organic phosphonate respectively represented by the following general formula (I) and (ll) T ll-O RI wherein R R R R R and R each are alkyl group having one to 20 carbon atoms, haloalkyl group having one to 20 carbon atoms, alkenyl group having one to 20 carbon atoms, arylalkyl group having seven to 20 carbon atoms, alkylaryl group having seven to 20 carbon atoms, or aryl group and may be the same with or different from each other and R may be hydrogen atom or at a temperature above C. at 

1. AN IMPROVED PROCESS FOR PRODUCING FLAME-RETARDANT ACRYLIC FIBER WHICH COMPRISES A. PREPARING ACRYLIC FIBERS IN A HYDROGEL CONDITION BY WETSPINNING A SPINNING SOLUTION, WHICH CONSISTS OF ACRYLONITRILE HOMO-OR -CO-POLYMERS AND A CONCENTRATED AQUEOUS SOLUTION OF THIOCYANATE, CONTAINING FINELY DISPERSED PARTICLES OF A HALOGEN-CONTAINING POLYMER SELECTED FROM THE GROUP OF HOMO- AND CO-POLYMERS OF VINYL HALIDE AND HOMO-AND CO-POLYMER OF VINYLIDENE HALIDE, B. TREATING SAID ACRYLIC FIBERS IN A HYDROGEL CONDITION WITH AT LEAST ONE ORGANIC COMPOUND, WHICH CAN DISSOLVE, SWELL OR PLASTICIZE THE HALOGEN-CONTAINING POLYMER, SELECTED FROM THE GROUP OF AN ORGANIC PHOSPHATE AND AN ORGANIC PHOSPHONATE RESPECTIVELY REPRESENTED BY THE FOLLOWING GENERAL FORMULAS (1) AND (11)
 2. The process of claim 1 wherein said acrylonitrile copolymer contains at least about 70 percent of acrylonitrile, by weight, based on the total weight of the polymer, and the balance of one or more comonomers copolymerizable therewith.
 3. The process of claim 1 wherein the halogen-containing polymer is polyvinyl chloride.
 4. The process of claim 1 wherein the halogen-containing polymer is a copolymer of vinyl chloride and vinylidene chloride.
 5. The process of claim 1 wherein an amount of halogen-containing polymer to add to the spinning solution is 10 to 120 percent by weight based on the weight of the acrylonitrile polymer present in the spinning solution.
 6. The process of claim 5 wherein the amount of halogen-containing polymer is 30 to 100 percent by weight based on the weight of acrylonitrile polymer present in the spinning solution.
 7. The process of claim 1 wherein said organic compound is selected from the group of tributyl phosphate, trioctyl phosphate, triphenylphosphate, tribenzyl phosphate, tricresyl phosphate, tris(2,3-dibromopropyl)phosphate, tris(2,3-dichloropropyl)phosphate, tris(chlorobromoethyl)phosphate, tris(bromochloropropyl)phosphate, tris(2-chloroethyl)phosphate, bisdibromopropyldichloropropyl phosphate, bisbromochloropropylbromochloropropyl phosphate, bisdibromopropylidibromopropyl phosphonate, bis-2-chloroethylvinyl phosphonate,
 8. The process of claim 1 wherein the amount of absorption of the organic compound in the fiber in such treatment is 10 to 80 percent by weight based on the weight of the halogen-containing polymer present in the fiber.
 9. An improved process for producing flame-retardant acrylic fibers which comprises a. preparing acrylic fibers in a hydrogel condition by wet-spinning a spinning solution, which consists of acrylonitrile homo- or co-polymerS and a concentrated aqueous solution of thiocyanate, containing finely dispersed particles of a halogen-containing polymer selected from the group of homo- and co-polymers of vinyl halide and homo- and co-polymers of vinylidene halide, b. treating said acrylic fibers in a hydrogel condition with at least one organic compound, which can dissolve, swell or plasticize the halogen-containing polymer, selected from the group of an organic phosphate and an organic phosphonate respectively represented by the following general formula (I) and (II)
 10. An improved process for producing flame-retardant acrylic fibers which comprises a. preparing acrylic fibers in a hydrogel condition by wet-spinning a spinning solution, which consists of acrylonitrile homo- or co-polymers and a concentrated aqueous solution of thiocyanate, containing finely dispersed particles of a halogen-containing polymer selected from the group of homo- and co-polymers of vinyl halide and homo- and co-polymers of vinylidene halide, b. treating said acrylic fibers in a hydrogel condition with at least one organic compound, which can dissolve, swell or plasticize the halogen-containing polymer, selected from the group of an organic phosphate and an organic phosphonate respectively represented by the following general formula (I) and (II) 